1. Field of the Invention
The invention relates to a process for easily degrading waste consisting of the reaction products of organic compounds, containing isocyanate groups, with alcohols and/or water. In particular, it relates to a process for easily degrading polyurethane waste.
2. Description of the Prior Art
Polyurethane waste is produced in relatively large amounts in the form of pieces of foam, for example, in the manufacture of upholstery components. Furthermore, polyurethane waste is obtained in the manufacture of hard-foam panels or shock-absorbing parts.
The elimination of polyurethane waste in foamed form is of particular interest since, because of its low density, this waste takes up a large volume and is difficult to store. Burning the waste leads to pollution of the environment and to the loss of the raw materials used to prepare the foam.
For this reason, various method have already been investigated for working up such polyurethane waste so as to recover the starting materials. For example, polyurethane foam waste has been subjected to the action of water at temperatures up to 400.degree. C. in a closed system. In this process, there is a partial hydrolytic degradation of the foam structure. The process, however, essentially has two disadvantages. A degradation product consisting of two phases is formed, one phase consisting essentially of the polyol component of the foam material and the other, essentially of the amine component of the foam material. The separation of the two phases is exceedingly difficult and can be incompletely carried out only.
Another disadvantage is that the polyol component which is to be reused for foaming, can be freed from the water it contains only by considerable effort. This residual water content interferes with the usefulness of the polyol as a foam-forming component. Also, the use of temperatures up to 400.degree. C. also promotes the formation of thermal degradation products of the foam material which impair the application properties of the polyol component which is to be reused.
Processes for improving this hydrolysis process have become known. For example, a process is described in German Offenlegungsschrift No. 23 62 921 for converting polyurethane foam into diamines and a liquid, polymeric hydrolysis product of the polyurethane, while at the same time separating the diamines from the liquid, polymeric hydrolysis product.
In this process:
(a) the polyurethane foam is introduced into a closed reaction zone kept at a temperature in the range of about 218.degree. to 400.degree. C. (425.degree. to 750.degree. F.),
(b) water vapor is introduced into the reaction zone in an amount sufficient for producing a pressure of about 0.5 to about 1.5 atmospheres at this temperature in the reaction zone,
(c) the gaseous outflow from the reaction zone, which contains the water vapor and the diamines, is removed and
(d) the liquid, polymeric hydrolysis product of the polyurethane is removed from the reaction zone.
While with this process the amine portion can be separated from the polyol component of the hydrolytically split foam material, a reaction temperature up to 400.degree. C. is still required. Moreover, the disadvantage of having to remove the water contained in the polyol before the latter is used again remains.
For this reason, attempts have been made to substitute a multifunctional alcohol for the water previously used in the degradation of the polyurethane foam. Success has been achieved if, for example, a linear, bifunctional alcohol, such as, ethylene glycol, is used instead of water. Once again, however, a degradation product is obtained which consists of two layers which are difficult to separate from one another.
The object of U.S. Pat. No. 3,983,087 is a process for the degradation of polyurethane foam waste to a homogeneous mixture of polyols by the use of branched alkylene glycols, such as, for example, 1,2-propylene glycol. In this process, the polyurethane foam is broken down using up to equal parts by weight of propylene glycol at temperatures of 180.degree. to 250.degree. C. to form a uniform, homogeneous phase. A significant disadvantage of this process is that the degradation product contains propylene glycol which interferes with the foam formation when the polyol obtained is used as a foam component. A preferred embodiment of the process described in U.S. Pat. No. 3,983,087 is to allow the alkylene oxide to react with the degradation product containing the propylene glycol in order the convert the propylene glycol into higher molecular weight compounds.
Finally, a process for the recovery of polyols from polyurethane is described in German Offenlegungsschrift No. 25 34 465. In this process, a polyurethane is dissolved in an aliphatic diol with a molecular weight of approximately 400 to 3,000 and a boiling point of at least 180.degree. C. and the mixture is heated in the presence of a halogenated phosphoric acid ester to approximately 170.degree. to 250.degree. C., the weight ratio of aliphatic diol to halogenated phosphoric acid ester being 1:1 to 20:1. The process is disadvantageous because a two-phase product is obtained from the working up, although the two phases can be separated relatively readily. For the working up, the relatively expensive halogenated phosphoric acid ester is required, which is not absolutely safe for physiological reasons.
Occasionally, it is also necessary to convert isocyanates which no longer can be used because of impurities or for other reasons, into a form in which they can be disposed of. For this purpose, they may be reacted with water. The conversion of these waste materials into industrially usable compounds is also desirable.